1. Field of the Invention
The invention relates to the field of electrophysiology and more particularly to the sensing of intracardiac electrical patterns, a mapping of intracardiac electrophysiology, and the use of such sensing and mapping for clinical treatment.
2. Description of the Prior Art
The prior focus of electrophysiology has been directed to identifying the mechanisms of heart arrhythmias and evaluation of drug and other therapies upon the observed arrhythmias. Current studies in electrophysiology have continued to evolve to identify localized areas of abnormal myocardium as the sources of arrhythmias and to selectively remove or otherwise deactivate the abnormal myocardium. Obliteration has generally been practiced through localized ablation, generally using a short range radio frequency diathermy technique, although other energy sources such as laser energy, ultrasound and/or cyroprecipitation may also be used.
The treatment of heart arrhythmias has thus become increasingly dependent upon the ability to identify the precise location or origin in the myocardium of the abnormal rhythms. The prior art practice for locating the abnormal myocardium is to dispose a catheter within the heart chamber carrying a standard array of ring and tip electrodes. Direct contact of the tip electrode is used for making an intracardiac electrogram in a manner similar to that which has been practiced for many years with respect to pacemaker sensing. See, Imran, "Endocardial Mapping and Ablation System and Catheter Probe", U.S. Pat. No. 5,156,151 (1992).
One of the problems in prior art pacemaking has been the ability to simultaneously monitor the activity within the heart chamber while a large ventricular stimulating pulse was delivered through the catheter tip. One prior art solution is shown in Goldreyer, U.S. Pat. No. 4,365,639, wherein orthogonal sensing electrodes positioned on the catheter in the atrium were able to sense heart activity without being overwhelmed or saturated by the large ventricular stimulating pulse delivered through the catheter tip. In other words, because of the orthogonal placement of the sensing electrodes within the catheter body relative to the stimulating tip and the differential signal processing from the orthogonal electrodes, signals in the heart from directions other than the tip of the catheter could be preferentially sensed shortly after the large pacing and responsive ventricular pulse without saturation of the sensing circuitry.
What is needed is a method and apparatus for reliably mapping discrete electrophysiologic activity in the heart without the need to contact the heart walls and which can be done simultaneously with pacing or ablation procedures.